1. Field of the Invention
The present invention relates to a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera associated with the external flash device.
2. Description of the Related Art
Conventionally, a flash-light emission of an external flash device is remotely controlled by a camera in accordance with a so-called slave method. Namely, when a flash light is emitted from a built-in flash device of the camera, the emitted flash light serves as a trigger for initiating an flash-light emission of the external flash device.
In this external flash control system, an amount of the flash-light emission of the external flash device cannot be accurately controlled, because only a timing of the flash-light emission of the external flash device is adjusted, with the amount of the flash-light emission being fixed. Thus, it is difficult to provide highly accurate exposure in response to photographing conditions which are variable depending on an object-distance or the like.
Therefore, an object of the present invention is to provide a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera, in which both a timing and an amount of the flash-light emission are properly and accurately controllable.
In accordance with an aspect of the present invention, there is provided a flash control system for remotely controlling an external flash device by a camera associated with the external flash device. In the flash control system, the camera includes a guide number calculator that calculates a guide number as an exposure factor for the external flash device, a light signal source that emits a light signal, and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the guide number is represented by the time interval between the at least two light signals. The external flash device includes a light signal detector that detects the at least two light signals emitted from the light signal source, and a flash-light emission controller that controls an amount of the flash-light emission of the external flash device in accordance with the time interval.
In the flash control system, the camera may be further includes a flash-light emission timing calculator that calculates a flash-light emission timing at which a flash-light should be emitted from the external flash device. In this case, the light signal controller further controls an emission of one of the at least two light signals such that the flash-light emission timing is represented by the emission of the one of the at least two light signals, and the flash-light emission controller further controls a timing of a flash-light emission of the external flash device in accordance with the emission of the one of the two light signals.
Preferably, the calculation of the guide number by the guide number calculator is based on a photometry measurement and an object-distance measurement performed by the camera.
Also, preferably, the light signal source comprises a flash lamp of a built-in flash device incorporated in the camera. The light signal controller may comprise a flash-light emission control circuit contained in the built-in flash device, and the flash-light emission control circuit includes an insulated-gate bipolar transistor for turning ON/OFF the flash lamp. The flash-light emission control circuit may includes a switcher which is arranged such that each of the at least two light signals is emitted as a light-pulse signal from the flash lamp by turning ON/OFF the flash lamp with the insulated-gate bipolar transistor.
Preferably, the light signal detector includes a light guide element for detecting a part of a flash-light emission of the external flash device, and the flash-light emission controller is constituted such that the amount of the flash-light emission of the external flash device is controlled on the basis of the detected part of the flash-light emission of the external flash device.
In accordance with another aspect of the present invention, there is provided an external flash device, which comprises a flash lamp that emits a flash-light, a light signal detector that detects at least two light signals emitted at a time interval representing a guide number as a photographic exposure factor, and a flash-light emission controller that controls an amount of the flash-light emission in accordance with the time interval between the at least two light signals.
Preferably, the external flash device further comprises a timing controller that controls a timing of the flash-light emission of the flash lamp on the basis of a detected-timing at which one of the at least two light signals is detected by the light signal detector.
In accordance with yet another aspect of the present invention, there is provided a camera, which comprises a guide number calculator that calculates a guide number as a photographic exposure factor for an external flash device, a light signal source that emits a light signal to the external flash device, and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the guide number is represented by the time interval between the at least two light signals.
Preferably, the camera further comprises a flash-light emission timing calculator that calculates a flash-light emission timing at which a flash-light should be emitted from the external flash device. In this case, the light signal controller further controls an emission of one of the at least two light signals such that the flash-light emission timing is represented by the emission of the one of the at least two light signals.